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Archive for July, 2010

Circuit Breaker Retrofitting Shortcut Mistake

July 16th, 2010 No comments
For many years retrofitting General Electric circuit breakers and Westinghouse, now Cutler Hammer, circuit breakers was very common.  Replacing the old dashpot style over current devices with modern electronic over current protection greatly improved the reliability and the flexibility of the retrofitted circuit breaker. This was particularly true when using the newer generation electronic retrofit kits. We still run into many of these retrofitted circuit breakers today.  Typically the retrofits were well done. But sometimes we run across a circuit breaker that was retrofitted in the field, on site. This saved time and was often done quickly during shutdowns or to just save cost. Ignoring the need to maintain a circuit breaker to be retrofitted, MIDWEST never retrofitted circuit breakers on site because of the need to perform complete over current testing and special load testing after the retrofit was complete.  Companies that retrofitted breakers on site could test the breaker by secondary injection method. That would prove the new electronic device operated properly and it would prove the old Westinghouse circuit breaker would actually trip, but it did not proof test the complete system. Worse yet were occasions when we might see a General Electric circuit breaker, for example, that had been retrofitted on site and not even tested by secondary injection method by the contractor that did the work.  MIDWEST recognizes this when we are troubleshooting a circuit breaker that apparently failed to trip and we discover that it would never trip under any circumstances.  We do a positive trip test. Tough test, takes about 12 seconds. We simply confirm that the trip device will actually move the trip bar enough to trip the Westinghouse circuit breaker, for example.  And we find out it will not. This is typically just a mechanical adjustment.  But you can imagine the anger when a customer finds out that the breaker they paid 2 or 3 thousand dollars or more to retrofit fifteen years ago, was just a switch because the breaker would never trip under any conditions, other than pushing the trip button.  Period maintenance and testing would have found this. Experience and knowledge would have prevented it. Shortcuts cause problems. It wouldn’t make any difference if it was an old Allis Chalmers, Siemens, ITE, or Federal Pacific or General Electric or Westinghouse circuit breaker, the problem was with the service company procedure, not the manufacturer.

All Wet Circuit Breakers

July 12th, 2010 No comments
TJJ436300 General Electric Circuit Breaker

TJJ436300 General Electric Circuit Breaker

MIDWEST buys surplus, old, used, obsolete, and even ugly circuit breakers.  We are paranoid about the history and condition of these previously owned circuit breakers.  We are particularly concerned someone will try to sell us breakers that look good, but have been damaged by water.  We are especially cautious because of dramatic flooding in recent years. This week we got a call asking us if we wanted to buy like new circuit breakers that were flooded with water.  Our polite answer was a screaming “No!”  They were honest and told us the breakers had been flooded.  We will not even consider buying moisture damaged circuit breakers. They could even be brand new circuit breakers and still, no. 

 

These breakers could be cleaned up cosmetically so they look new and they might even pass the basic electrical tests, but we know they are still junk. If you tore a water damaged breaker completely apart, including the trip device and the operating mechanism, you would find rust and caked on dirt, even mud.  Under the stationary contacts, on the trip device hold down bolts, under the trip element, inside the trip element, everywhere in and under the operating mechanism.

 

The breaker may pass the insulation resistance tests, the contact resistance tests, and maybe even the over current tests. And, if you don’t bother to take the cover off, you might never know that the breaker was damaged by water or extreme humidity.  We know that plants that have been flooded will go through a thorough switchgear on site reconditioning process. Switchgear, including circuit breakers, will be restored to operating condition in an effort to get the power back on as quickly as possible. But these are emergency situations and getting replacement equipment quickly may not be possible.  So one should not compare such an extreme circumstance with the normal world of a Switchgear Service Shop. 

 

We want to know the history of equipment we purchase and we can not rely on that information being always accurate. Everything must be completely checked out, reconditioned.  And because equipment passes standardized tests, does not mean it is reliable for reuse.  Reconditioning will determine if it will be reliable after passing the standardize tests and MIDWEST’s other reliability centered tests. But testing alone does not determine reliability.

Aluminum Feeders Damage Old Circuit Breakers

July 2nd, 2010 No comments

MIDWEST had a customer that seemed to call us about every 5 to 6 months for a replacement circuit breaker. This went on for about three years, before we noticed the pattern. We recognized it because he started calling the same Engineer.   We asked why he needed so many reconditioned replacement circuit breakers over the past two or three years. It seems their facility was built in the 1970s when copper was so scarce and expensive that many projects were built using aluminum cables.  Unfortunately some installations did not use the correct lugs or failed to install the lugs properly. We were very surprised they didn’t have these problems, or worse, decades ago.  We asked them if they still had a couple of the old damaged circuit breakers laying around.  Could they send us one or more of the old circuit breakers that had been damaged, so we could inspect them and give some recommendations on how to prevent future problems.  Inspection of two of their used circuit breakers that had failed, showed extensive heat and arcing damage at one or more of the load side lugs.  We have seen this type damage many times and it invariably was caused by cables that had become loose inside the lug or lugs that had become loose at the breaker connection.  One of our senior engineers worked in electrical construction during the years aluminum cables were used.  He explained how this could be dangerous and he also was very surprised they didn’t have problems many years ago.  He said a lot of new circuit breakers and MLO, ie main lugs only, panel boards were damaged when the aluminum cable terminations failed in the years after installation. He had one strong recommendation.  Hire an old time electrician who remembers those days and knows from experience what has to be done to correct things.  He said this can be a challenge. But, if they don’t do something, they may lose more than an occasional old circuit breaker. He also said to be extremely careful when installing a replacement circuit breaker. Always turn all the power off, including the feeder into the old power panel or panelboard. Safety first.